Second Step: Try a blank Morphic World. Choose "Do" from the main menu (middle button down in Squeak's background), then choose "WorldMorph new open". (You can also do this from the Workspace.) Use middle-button menu in the new Morphic world to choose "New morph" then add morphs. I find the BouncingAtomsMorph in Demos submenu cool, and the RecordingControls in the Widgets submenu really neat.

Third Step: Build a Morph. I've used Janak's stuff to play with making new morphs, but haven't really figured it all out (Janak on Morphic UI). It looks relatively simple. Basically, you have to initialize to create yourself, then respond to step if you want anything to happen dynamically. There's more to the API, but that seems to be enough to get something going.